The present invention is directed to electronic lighting systems, and more particularly to an integrated bridge inverter circuit used in connection with a discharge lamp.
Existing single-stage high-power factor electronic ballasts designed for discharge lamps, such as integral compact fluorescent lamp applications have various drawbacks including an undesirably limited zero-voltage switching range, a high unnecessary component stress during operation and starting. Existing systems also have undesirably high crest factors and high harmonics"" content, which prevents product from compliance with International Electrotechnical Commission (e.g. IEC-61000-3-2) standards.
One existing electronic ballast which may be used for discharge lamps is shown for example, by Wong, U.S. Pat. No. 5,426,344. Wong discloses a self-oscillating high-power factor electronic ballast. The disclosed Wong circuit, as well as other existing ballasts, use input bridge circuit portions and inverter circuit portions which are distinct and separate from each other. The approach proposed in Wong et al. has a crest factor of 2.0 or higher, with high bus-voltage stresses, such as the voltage across C3, which in turn requires high voltage-rated transistors. A further disadvantage of this approach is a need to use of large EMI filter due to a discontinuous nature of the input current existing prior to the input bridge D1. The high-peak currents, which have higher high frequency current content, need to be filtered out by the input EMI filter. Therefore, yet a further disadvantage of existing ballasts such as Wong et al., is a high current stress on the switch transistors and resonant components.
To overcome shortcomings of existing prior art ballasts it has been deemed desirable to develop a ballast having a high power factor, low total harmonic distortion, and yet having an extended zero-voltage switching range, low cost, and low component stresses.
A ballast, powered by a power source is used to control operation of a load such as a discharge lamp. The ballast includes a switching network configured to control a supply of power to the load, and a bridge converter network which is configured to receive an input signal from the power source and convert it into a form useable by the switching network. The bridge converter network is integrated into the switching network.